The present invention relates generally to packaging electronic components, and particularly to methods of encapsulating board-on-chip (BOC) ball grid array (BGA) integrated circuit die units, and particularly to die units with non-standard bond pad layouts including an I-shaped bond pad layout.
Integrated circuit (IC) chips are enclosed in plastic packages that provide protecting against damage and environmental contaminants, and enable electrical of the chip to other circuits on a printed circuit board. Packaging IC chips has involved the placement of a chip on a flexible board where following adhesion of the chip to the board and wire bonding to connect the leads from the chip to the terminals on the board, an encapsulant is flowed over the chip and board to form a sealed package.
Plastic encapsulation of semiconductor devices by transfer molding is a conventionally used technique. Typically, a pre-encapsulated die unit is placed in a mold having top and bottom cavity molding plates. The lower molding plate has a constricted channel or mold gate along one side of the plate, and the encapsulation material, typically a thermoplastic or thermosetting material, enters through the mold gate and flows under and then over the IC chip to cover the electrical leads. The mold gate limits the flow rate and injection velocity of a molding compound into the cavity. The encapsulation material is then cured to harden it. In devices having a ball grid array (BGA) on one side of the substrate, the molding process is conducted so that the ball grid array connections are not covered by the molding compound during the encapsulation process.
The assembly process flows of standard BOC BGA packaging techniques are set-up for conventional IC chips having a bond pad layout arranged in a column down the center of the chip. Such packaging techniques cannot accommodate the assembly of die packages that do not utilize a standard wire bond slot and bond pad layout.
Currently, a semiconductor chip having a non-standard bond pad layout is packaged in a chip-on-board (COB) ball grid array (BGA) package. A disadvantage in using a COB BGA packaging technique is the use of long wires for connecting the bond pads in the center of the die to contacts on the underlying substrate, which are prone to damage. Another drawback is the resulting larger package size, which is needed to allow sufficient space for the wire bond connections.
In view of these and other deficiencies in conventional methods for fabricating BGA packages, improvements in fabrication methods for BOC BGA packages are needed.
The present invention provides semiconductor assemblies for forming BOC BGA packages, methods of encapsulating a semiconductor die unit, a mold assembly for use in the method, and resulting encapsulated die packages. In particular, the invention provides a semiconductor die unit comprising an integrated circuit die with a plurality of bond pads in an I-shaped layout and an overlying support substrate having an I-shaped wire bond slot.
In one aspect, the invention provides a method of encapsulating an integrated circuit die unit. In one embodiment, the method comprises providing a mold containing a die unit; the mold having first and second molding plates, a molding chamber, and a mold gate through the first molding plate providing a conduit for flowing a molding compound into the chamber, the mold gate oriented perpendicular to the second molding plate; the die unit comprising a die mounted onto a support substrate, the die having a first surface, a second surface, and sides, the first surface of the die comprising a plurality of bond pads formed thereon, and mounted onto the support substrate with the bond pads exposed through an opening of the support substrate; the die unit positioned within the mold such that the mold gate is oriented perpendicular to the opening in the support substrate of the die unit; and introducing a molding compound through the mold gate to flow the molding compound into the opening in the support substrate of the die unit to enclose the bond pads on the die.
In another embodiment, the method comprises providing a mold having a molding chamber and a mold gate providing a conduit for introducing a molding compound into the chamber, providing a die unit comprising a die having a first (active) surface, a second (inactive) surface, and sides, with the first surface of the die having electrical elements and a plurality of bond pads disposed thereon, the die mounted onto a support substrate with the bond pads exposed through an opening of the support substrate; placing the die unit in the mold with the mold gate oriented perpendicular to the first surface of the die; and introducing a molding compound through the mold gate whereby the molding compound flows into the opening in the support substrate to enclose the electrical elements and bond pads on the die.
In another embodiment of the method, the molding compound can be flowed onto the sides of the die and, optionally, onto the second (inactive) surface of the die, for example, through a gap or hole in the substrate of the die unit. In another embodiment of the method, the molding compound can be delivered through the mold gate onto a die unit at various positions along the wire bond slot, for example, at or near one end of the wire bond slot to about the center of the slot, and the compound flowed to fill the opening. In other embodiments of the method, the molding compound can be delivered into the mold chamber and into the wire bond slot opening in a downward or in an upward direction, for example, by orienting the mold gate and die unit relative to each other to achieve the desired upward or downward flow. In yet another embodiment, the method can be used for encapsulating a BOC BGA die unit having a wire bond slot and a plurality of bond pads in an I-shaped configuration or other non-standard layout.
In another embodiment, the method comprises the steps of: providing a die comprising a first surface, a second surface, and opposing sides, the first surface having electrical elements and a plurality of bond pads disposed thereon in an I-shaped layout; mounting the die onto a support substrate with the bond pads exposed through an I-shaped wire bond slot of the support substrate; electrically connecting the bond pads through the opening to bond pad fingers mounted on the support substrate adjacent to the opening to form a pre-encapsulated die unit; providing a mold having a molding chamber and a mold gate providing a conduit for introducing a molding compound into the chamber; placing the die unit in the mold with the mold gate oriented perpendicular to the opening of the support substrate of the die unit; and introducing a molding compound through the mold gate to flow the molding compound into the opening of the support substrate to enclose the electrical elements and bond pads on the first surface of the die. In another embodiment, the die is mounted onto the support substrate to provide a gap between a peripheral edge of the die and the opening of the support substrate; and in the step of introducing the molding compound, the molding compound flows through the gap and onto at least the sides of the die. In yet another embodiment, the support substrate includes holes therethrough adjacent to the gaps, and the die is mounted onto the support substrate such that the holes through the support substrate are uncovered, and the molding compound is flowed through the gap and the holes in the substrate to cover at least the sides of the die.
In another aspect, the invention provides a mold for encapsulating a semiconductor die. In one embodiment, the mold comprises first and second molding plates, a chamber, and a mold gate providing a conduit for introducing a molding compound into the chamber, with the mold gate oriented in a first molding plate to deliver a molding compound into the chamber perpendicularly into a wire bond slot of a die unit positioned between the two plates of the mold. The mold gate in the first molding plate is oriented perpendicular to the second molding plate, and perpendicular to the wire bond slot of the support substrate of the die unit positioned in the mold. The mold gate can positioned as desired within a molding plate to deliver the molding compound onto a die unit at or near one end of the wire bond slot to about the center of the slot, and the molding compound flowed to fill the opening. The mold gate and die unit can also be oriented to deliver the molding compound into the mold chamber in a downward or an upward direction into the wire bond slot opening. The mold can be structured to inhibit or allow flowing of the molding compound onto the sides and, optionally, the second (inactive) surface of the die.
In another aspect, the invention provides a semiconductor assembly. In one embodiment, the assembly comprises a board-on-chip (BOC) ball grid array (BGA) die unit having a die with a plurality of bond pads in an I-shaped layout exposed through an I-shaped wire bond slot of an overlying support substrate. The die unit can further include an adhesive layer interposed between the die and the support substrate, for example, an adhesive sheet having an I-shaped opening corresponding to the opening of the support substrate, or a pair of adhesive strips positioned on opposite sides and adjacent to the I-shaped opening.
In another embodiment, the die unit can include a feature such as a gap or a hole through which a molding compound can flow onto the sides of the die and, optionally, onto the inactive surface of the die, when the die unit is placed into a mold for encapsulation. In one example, the support substrate (and die) can be dimensioned (and configured) such that mounting the die onto the support substrate provides a gap between a peripheral edge of the die and the wire bond slot of the support substrate. In another example, a hole can be provided adjacent the wire bond slot to provide an opening through the support substrate. The die unit can be partially encapsulated with only the active surface of the die and, optionally, the sides of the die encapsulated with a molding compound, and the inactive surface of the die exposed. The die unit can also be completely overmolded by a molding compound.
The invention advantageously provides a BOC BGA package for IC dies and chips having an I-shaped bond pad configuration or other non-standard layout, and an assembly process to build such a package. The present BOC BGA semiconductor package is easier to assembly than COB BGA packages, particularly in terms of wire bonding and molding processes, and achieves a smaller package size with improved electrical performance due to shorter wire lengths. In addition, the BOC BGA packaging maintains a conventional solder ball grid array to facilitate its use in conventional semiconductor assemblies. The present invention can be applied to both single-in-line strip (SIS) BOC configurations in which the arrangement of units within the strip is limited to a single row, and matrix BOC configurations in which the strip configuration is in an array form and the arrangement of units is not limited to a single row.